Just started playing this again with a friend (level 11 at mo) and I had the mission stop the gorn advance but I can't enter the Argelius system? I get no prompt asking me to enter it...
Any idea why?
Its possible you're at the wrong system. According to STO wiki, the only mission involving Argelius System
is to pick up a passenger for Treasure Trading Station
Perhaps if you can tell us the name of the mission you are currently on, we can point you in the right direction.